Price 129,00 €
Why Brewster Angle?
The Lacerta 1.25 "Herschel prism with Brewster angle has some advantages over 90 degree prisms. Since the polarization at Brewster angles is almost 100%, the Lacerta Herschel prism with the mandatory ND3 neutral density filter AND with an additional polar filter enables practically full light attenuation - in reality a dimming range between ND4.07 and 6.37 - mostly even more. Without a polar filter, the Herschel prism works at the lowest light attenuation (ND4.07) and can thus be used for photography. With the "traditional" 90 degree Herschel prisms, this value is only between 4.24 and 5.00.
The visual perception at different neutral densities is shown in the picture below. It is easy to see that the granulation in traditional Herschel prisms can only be observed well with an additional THIRD filter (ND3 and polarizing filter are required!). Herschel prisms with Brewster angle do not need an additional filter because the dimming range is continuously possible up to ND6.37!
How do you use the 1.25 "Herschel prism?
- The ND3 filter and the polarizing filter are simply screwed into the eyepiece, the overall brightness is adjusted by turning the eyepiece.
- Please note that the optical elements must strictly have the following order: telescope - Herschel prism - ND3 filter - polar filter - additional filter (e.g. UV / IR block or contrast filter of your choice) - eyepiece (or camera)
- When changing the eyepiece, it is essential to ensure that all filters are screwed around and reassembled in the correct order.
Why is the Lacerta Herschel prism open at the bottom?
- The open design allows much better ventilation than other Herschel wedges on the market
- The proportion of scattered light that comes through the opening is negligible against the sun from the telescope
- No shoes will catch fire as no light escapes through the opening
WARNING! The image through the Herschel wedge is relatively bright without an ND3 filter. The Herschel wedge itself only filters 92-95% of sunlight. Because of this, an ND3 filter is mandatory! This filter is included in the ready-to-use package.
WARNING! Do not use the Herschel wedge with Newtonian, Maksutov or Schmidt-Cassegrain telescopes. The heat can damage the internal parts in these telescopes.
These terms and conditions are valid from November 7th, 2020.
Astro Art Finland
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Astro Art Finland
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